My eye was drawn to the pattern of guano on the cliffs below Hope's Heugh near St Abbs Head, Scotland.

The diagonals are created by guillemots, the ultimate rock artists. They lay eggs on the bare cliff face and incubate them for at least a month. They then have to protect the chick for 3 or 4 more weeks. All that time, they face the cliff wall to protect against opportunist crows and gulls. Fancy spending two months facing a wall? Creating patterns on the cliff face is probably the only entertainment on offer.